linux-kernel - Re: [PATCH 2/3] nvme: Retrieve the required IO queue entry size from the controller

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Message-ID: <20190716120547.GA2388@lst.de>
Date:   Tue, 16 Jul 2019 14:05:47 +0200
From:   Christoph Hellwig <hch@....de>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     Christoph Hellwig <hch@....de>, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Jens Axboe <axboe@...com>,
        Keith Busch <kbusch@...nel.org>, Paul Pawlowski <paul@...rm.io>
Subject: Re: [PATCH 2/3] nvme: Retrieve the required IO queue entry size
 from the controller

On Tue, Jul 16, 2019 at 08:58:28PM +1000, Benjamin Herrenschmidt wrote:
> The main risk is if existing controllers return crap in SQES and we try
> to then use that crap. The rest should essentially be NOPs.
> 
> Maybe I should add some kind of printk to warn in case we use/detect a
> non-standard size. That would help diagnosing issues.

Given that the spec currently requires bits 0 to 3 of SQES to be 6
we might as well not check SQES and just hardcode it to 6 or 7 depending
on the quirk.  That actually was my initial idea, I just suggested using
the SQES naming and indexing.